Transcriptional regulation of APH-1A and increased gamma-secretase cleavage of APP and Notch by HIF-1 and hypoxia

Melatonin Inhibits Hypoxia-Induced Alzheimer's Disease Pathogenesis by Regulating the Amyloidogenic Pathway in Human Neuroblastoma Cells

Stroke and Alzheimer's disease (AD) are prevalent age-related diseases; however, the relationship between these two diseases remains unclear. In this study, we aimed to investigate the ability of melatonin, a hormone produced by the pineal gland, to alleviate the effects of ischemic stroke leading to AD by observing the pathogenesis of AD hallmarks. We utilized SH-SY5Y cells under the conditions of oxygen-glucose deprivation (OGD) and oxygen-glucose deprivation and reoxygenation (OGD/R) to establish ischemic stroke conditions. We detected that hypoxia-inducible factor-1α (HIF-1α), an indicator of ischemic stroke, was highly upregulated at both the protein and mRNA levels under OGD conditions. Melatonin significantly downregulated both HIF-1α mRNA and protein expression under OGD/R conditions. We detected the upregulation of β-site APP-cleaving enzyme 1 (BACE1) mRNA and protein expression under both OGD and OGD/R conditions, while 10 µM of melatonin attenuated these effects and inhibited beta amyloid (Aβ) production. Furthermore, we demonstrated that OGD/R conditions were able to activate the BACE1 promoter, while melatonin inhibited this effect. The present results indicate that melatonin has a significant impact on preventing the aberrant development of ischemic stroke, which can lead to the development of AD, providing new insight into the prevention of AD and potential stroke treatments.

Detrimental Roles of Hypoxia-Inducible Factor-1α in Severe Hypoxic Brain Diseases

Hypoxia stabilizes hypoxia-inducible factors (HIFs), facilitating adaptation to hypoxic conditions. Appropriate hypoxia is pivotal for neurovascular regeneration and immune cell mobilization. However, in central nervous system (CNS) injury, prolonged and severe hypoxia harms the brain by triggering neurovascular inflammation, oxidative stress, glial activation, vascular damage, mitochondrial dysfunction, and cell death. Diminished hypoxia in the brain improves cognitive function in individuals with CNS injuries. This review discusses the current evidence regarding the contribution of severe hypoxia to CNS injuries, with an emphasis on HIF-1α-mediated pathways. During severe hypoxia in the CNS, HIF-1α facilitates inflammasome formation, mitochondrial dysfunction, and cell death. This review presents the molecular mechanisms by which HIF-1α is involved in the pathogenesis of CNS injuries, such as stroke, traumatic brain injury, and Alzheimer's disease. Deciphering the molecular mechanisms of HIF-1α will contribute to the development of therapeutic strategies for severe hypoxic brain diseases.

Inhibition of γ-secretase/Notch pathway as a potential therapy for reversing cancer drug resistance

The mechanism of tumor drug resistance is complex and may involve stem cell maintenance, epithelial-mesenchymal transition, the activation of survival signaling pathways, transporter protein expression, and tumor microenvironment remodeling, all of which are linked to γ-secretase/Notch signaling. Increasing evidence has shown that the activation of the γ-secretase/Notch pathway is a key driver of cancer progression and drug resistance development and that γ-secretase inhibitors (GSIs) may be the most promising agents for reversing chemotherapy resistance of tumors by targeting the γ-secretase/Notch pathway. Here, we systematically summarize the roles in supporting γ-secretase/Notch activation-associated transformation of cancer cells into cancer stem cells, promotion of the EMT process, PI3K/Akt, MEK/ERK and NF-κB activation, enhancement of ABC transporter protein expression, and TME alteration in mediating tumor drug resistance. Subsequently, we analyze the mechanism of GSIs targeting the γ-secretase/Notch pathway to reverse tumor drug resistance and propose the outstanding advantages of GSIs in treating breast cancer drug resistance over other tumors. Finally, we emphasize that the development of GSIs for reversing tumor drug resistance is promising.

Oxygen metabolism abnormality and Alzheimer's disease: An update

Oxygen metabolism abnormality plays a crucial role in the pathogenesis of Alzheimer's disease (AD) via several mechanisms, including hypoxia, oxidative stress, and mitochondrial dysfunction. Hypoxia condition usually results from living in a high-altitude habitat, cardiovascular and cerebrovascular diseases, and chronic obstructive sleep apnea. Chronic hypoxia has been identified as a significant risk factor for AD, showing an aggravation of various pathological components of AD, such as amyloid β-protein (Aβ) metabolism, tau phosphorylation, mitochondrial dysfunction, and neuroinflammation. It is known that hypoxia and excessive hyperoxia can both result in oxidative stress and mitochondrial dysfunction. Oxidative stress and mitochondrial dysfunction can increase Aβ and tau phosphorylation, and Aβ and tau proteins can lead to redox imbalance, thus forming a vicious cycle and exacerbating AD pathology. Hyperbaric oxygen therapy (HBOT) is a non-invasive intervention known for its capacity to significantly enhance cerebral oxygenation levels, which can significantly attenuate Aβ aggregation, tau phosphorylation, and neuroinflammation. However, further investigation is imperative to determine the optimal oxygen pressure, duration of exposure, and frequency of HBOT sessions. In this review, we explore the prospects of oxygen metabolism in AD, with the aim of enhancing our understanding of the underlying molecular mechanisms in AD. Current research aimed at attenuating abnormalities in oxygen metabolism holds promise for providing novel therapeutic approaches for AD.

γ-Secretase fanning the fire of innate immunity

Innate immunity is the first line of defense against pathogens, alerting the individual cell and surrounding area to respond to this potential invasion. γ-secretase is a transmembrane protease complex that plays an intricate role in nearly every stage of this innate immune response. Through regulation of pattern recognition receptors (PRR) such as TREM2 and RAGE γ-secretase can modulate pathogen recognition. γ-secretase can act on cytokine receptors such as IFNαR2 and CSF1R to dampen their signaling capacity. While γ-secretase-mediated regulated intramembrane proteolysis (RIP) can further moderate innate immune responses through downstream signaling pathways. Furthermore, γ-secretase has also been shown to be regulated by the innate immune system through cytokine signaling and γ-secretase modulatory proteins such as IFITM3 and Hif-1α. This review article gives an overview of how γ-secretase is implicated in innate immunity and the maintenance of its responses through potentially positive and negative feedback loops.

The Pleiotropic Face of CREB Family Transcription Factors

cAMP responsive element-binding protein (CREB) is one of the most intensively studied phosphorylation-dependent transcription factors that provide evolutionarily conserved mechanisms of differential gene expression in vertebrates and invertebrates. Many cellular protein kinases that function downstream of distinct cell surface receptors are responsible for the activation of CREB. Upon functional dimerization of the activated CREB to cis-acting cAMP responsive elements within the promoters of target genes, it facilitates signal-dependent gene expression. From the discovery of CREB, which is ubiquitously expressed, it has been proven to be involved in a variety of cellular processes that include cell proliferation, adaptation, survival, differentiation, and physiology, through the control of target gene expression. In this review, we highlight the essential roles of CREB proteins in the nervous system, the immune system, cancer development, hepatic physiology, and cardiovascular function and further discuss a wide range of CREB-associated diseases and molecular mechanisms underlying the pathogenesis of these diseases.

HIG1 domain family member 1A is a crucial regulator of disorders associated with hypoxia

Mitochondria play a central role in cellular energy conversion, metabolism, and cell proliferation. The regulation of mitochondrial function by HIGD1A, which is located on the inner membrane of the mitochondria, is essential to maintain cell survival under hypoxic conditions. In recent years, there have been shown other cellular pathways and mechanisms involving HIGD1A diametrically or through its interaction. As a novel regulator, HIGD1A maintains mitochondrial integrity and enhances cell viability under hypoxic conditions, increasing cell resistance to hypoxia. HIGD1A mainly targets cytochrome c oxidase by regulating downstream signaling pathways, which affects the ATP generation system and subsequently alters mitochondrial respiratory function. In addition, HIGD1A plays a dual role in cell survival in distinct degree hypoxia regions of the tumor. Under mild and moderate anoxic areas, HIGD1A acts as a positive regulator to promote cell growth. However, HIGD1A plays a role in inhibiting cell growth but retaining cellular activity under severe anoxic areas. We speculate that HIGD1A engages in tumor recurrence and drug resistance mechanisms. This review will focus on data concerning how HIGD1A regulates cell viability under hypoxic conditions. Therefore, HIGD1A could be a potential therapeutic target for hypoxia-related diseases.

HIF-1α Causes LCMT1/PP2A Deficiency and Mediates Tau Hyperphosphorylation and Cognitive Dysfunction during Chronic Hypoxia

Chronic hypoxia is a risk factor for Alzheimer's disease (AD), and the neurofibrillary tangle (NFT) formed by hyperphosphorylated tau is one of the two major pathological changes in AD. However, the effect of chronic hypoxia on tau phosphorylation and its mechanism remains unclear. In this study, we investigated the role of HIF-1α (the functional subunit of hypoxia-inducible factor 1) in tau pathology. It was found that in Sprague-Dawley (SD) rats, global hypoxia (10% O₂, 6 h per day) for one month induced cognitive impairments. Meanwhile it induced HIF-1α increase, tau hyperphosphorylation, and protein phosphatase 2A (PP2A) deficiency with leucine carboxyl methyltransferase 1(LCMT1, increasing PP2A activity) decrease in the rats' hippocampus. The results were replicated by hypoxic treatment in primary hippocampal neurons and C6/tau cells (rat C6 glioma cells stably expressing human full-length tau441). Conversely, HIF-1α silencing impeded the changes induced by hypoxia, both in primary neurons and SD rats. The result of dual luciferase assay proved that HIF-1α acted as a transcription factor of LCMT1. Unexpectedly, HIF-1α decreased the protein level of LCMT1. Further study uncovered that both overexpression of HIF-1α and hypoxia treatment resulted in a sizable degradation of LCMT1 via the autophagy--lysosomal pathway. Together, our data strongly indicated that chronic hypoxia upregulates HIF-1α, which obviously accelerated LCMT1 degradation, thus counteracting its transcriptional expression. The increase in HIF-1α decreases PP2A activity, finally resulting in tau hyperphosphorylation and cognitive dysfunction. Lowering HIF-1α in chronic hypoxia conditions may be useful in AD prevention.

Spatial Analysis of Neural Cell Proteomic Profiles Following Ischemic Stroke in Mice Using High-Plex Digital Spatial Profiling

Stroke is ranked as the fifth leading cause of death and the leading cause of adult disability in the USA. The progression of neuronal damage after stroke is recognized to be a complex integration of glia, neurons, and the surrounding extracellular matrix, therefore potential treatments must target the detrimental effects created by these interactions. In this study, we examined the spatial cellular and neuroinflammatory mechanisms occurring early after ischemic stroke utilizing Nanostring Digital Spatial Profiling (DSP) technology. Male C57bl/6 mice were subjected to photothrombotic middle cerebral artery occlusion (MCAO) and sacrificed at 3 days post-ischemia. Spatial distinction of the ipsilateral hemisphere was studied according to the regions of interest: the ischemic core, peri-infarct tissues, and peri-infarct normal tissue (PiNT) in comparison to the contralateral hemisphere. We demonstrated that the ipsilateral hemisphere initiates distinct spatial regulatory proteomic profiles with DSP technology that can be identified consistently with the immunohistochemical markers, FJB, GFAP, and Iba-1. The core border profile demonstrated an induction of neuronal death, apoptosis, autophagy, immunoreactivity, and early degenerative proteins. Most notably, the core border resulted in a decrease of the neuronal proteins Map2 and NeuN; an increase in the autophagy proteins BAG3 and CTSD; an increase in the microglial and peripheral immune invasion proteins Iba1, CD45, CD11b, and CD39; and an increase in the neurodegenerative proteins BACE1, APP, amyloid β 1-42, ApoE, and hyperphosphorylated tau protein S-199. The peri-infarct region demonstrated increased astrocytic, immunoreactivity, apoptotic, and neurodegenerative proteomic profiles, with an increase in BAG3, GFAP, and hyperphosphorylated tau protein S-199. The PiNT region displayed minimal changes compared to the contralateral cortex with only an increase in GFAP. In this study, we showed that mechanisms known to be associated with stroke, such as apoptosis and inflammation, occur in distinct spatial domains of the injured brain following ischemia. We also demonstrated the dysregulation of specific autophagic pathways that may lead to neurodegeneration in peri-infarct brain tissues. Taken together, these data suggest that identifying post-ischemic mechanisms occurring in a spatiotemporal manner may lead to more precise targets for successful therapeutic interventions to treat stroke.

Hypoxia Inducible Factor-1α binds and activates γ-secretase for Aβ production under hypoxia and cerebral hypoperfusion

Hypoxic-ischemic injury has been linked with increased risk for developing Alzheimer's disease (AD). The underlying mechanism of this association is poorly understood. Here, we report distinct roles for hypoxia-inducible factor-1α (Hif-1α) in the regulation of BACE1 and γ-secretase activity, two proteases involved in the production of amyloid-beta (Aβ). We have demonstrated that Hif-1α upregulates both BACE1 and γ-secretase activity for Aβ production in brain hypoxia-induced either by cerebral hypoperfusion or breathing 10% O2. Hif-1α binds to γ-secretase, which elevates the amount of active γ-secretase complex without affecting the level of individual subunits in hypoxic-ischemic mouse brains. Additionally, the expression of full length Hif-1α increases BACE1 and γ-secretase activity in primary neuronal culture, whereas a transcriptionally incompetent Hif-1α variant only activates γ-secretase. These findings indicate that Hif-1α transcriptionally upregulates BACE1 and nontranscriptionally activates γ-secretase for Aβ production in hypoxic-ischemic conditions. Consequently, Hif-1α-mediated Aβ production may be an adaptive response to hypoxic-ischemic injury, subsequently leading to increased risk for AD. Preventing the interaction of Hif-1α with γ-secretase may therefore be a promising therapeutic strategy for AD treatment.

Activation of the hypoxia response protects mice from amyloid-β accumulation

Alzheimer's disease (AD) is the most common cause of dementia with limited treatment options affecting millions of people and the prevalence increasing with the aging population. The current knowledge on the role of the hypoxia/hypoxia-inducible factor (HIF) in the AD pathology is restricted and controversial. We hypothesized based on benefits of the genetic long-term inactivation of HIF prolyl 4-hydroxylase-2 (HIF-P4H-2) on metabolism, vasculature and inflammatory response that prolonged moderate activation of the hypoxia response could hinder AD pathology. We used an aging model to study potential spontaneous accumulation of amyloid-β (Aβ) in HIF-P4H-2-deficient mice and a transgenic APP/PSEN1 mouse model subjected to prolonged sustained environmental hypoxia (15% O2 for 6 weeks) at two different time points of the disease; at age of 4 and 10 months. In both settings, activation of the hypoxia response reduced brain protein aggregate levels and this associated with higher vascularity. In the senescent HIF-P4H-2-deficient mice metabolic reprogramming also contributed to less protein aggregates while in APP/PSEN1 mice lesser Aβ associated additionally with hypoxia-mediated favorable responses to neuroinflammation and amyloid precursor protein processing. In conclusion, continuous, non-full-scale activation of the HIF pathway appears to mediate protection against neurodegeneration via several mechanisms and should be studied as a treatment option for AD.

Notch Signaling and Cross-Talk in Hypoxia: A Candidate Pathway for High-Altitude Adaptation

Hypoxia triggers complex inter- and intracellular signals that regulate tissue oxygen (O₂) homeostasis, adjusting convective O₂ delivery and utilization (i.e., metabolism). Human populations have been exposed to high-altitude hypoxia for thousands of years and, in doing so, have undergone natural selection of multiple gene regions supporting adaptive traits. Some of the strongest selection signals identified in highland populations emanate from hypoxia-inducible factor (HIF) pathway genes. The HIF pathway is a master regulator of the cellular hypoxic response, but it is not the only regulatory pathway under positive selection. For instance, regions linked to the highly conserved Notch signaling pathway are also top targets, and this pathway is likely to play essential roles that confer hypoxia tolerance. Here, we explored the importance of the Notch pathway in mediating the cellular hypoxic response. We assessed transcriptional regulation of the Notch pathway, including close cross-talk with HIF signaling, and its involvement in the mediation of angiogenesis, cellular metabolism, inflammation, and oxidative stress, relating these functions to generational hypoxia adaptation.

Aberrant role of pyruvate kinase M2 in the regulation of gamma-secretase and memory deficits in Alzheimer's disease

Toxic amyloid beta (Aβ) species cause synaptic dysfunction and neurotoxicity in Alzheimer's disease (AD). As of yet, however, there are no reported regulators for gamma-secretase, which links a risky environment to amyloid accumulation in AD. Here, we report that pyruvate kinase M2 (PKM2) is a positive regulator of gamma-secretase under hypoxia. From a genome-wide functional screen, we identify PKM2 as a gamma-secretase activator that is highly expressed in the brains of both patients and murine models with AD. PKM2 regulates Aβ production and the amount of active gamma-secretase complex by changing the gene expression of aph-1 homolog. Hypoxia induces PKM2 expression, thereby promoting gamma-secretase activity. Moreover, transgenic expression of PKM2 in 3xTg AD model mice enhances hippocampal production of Aβ and exacerbates the impairment of spatial and recognition memory. Taken together, these findings indicate that PKM2 is an important gamma-secretase regulator that promotes Aβ production and memory impairment under hypoxia.

Recent Progress in the Drug Development for the Treatment of Alzheimer's Disease Especially on Inhibition of Amyloid-peptide Aggregation

As the world 's population is aging, Alzheimer's disease (AD) has become a big concern since AD has started affecting younger people and the population of AD patients is increasing worldwide. It has been revealed that the neuropathological hallmarks of AD are typically characterized by the presence of neurotoxic extracellular amyloid plaques in the brain, which are surrounded by tangles of neuronal fibers. However, the causes of AD have not been completely understood yet. Currently, there is no drug to effectively prevent AD or to completely reserve the symptoms in the patients. This article reviews the pathological features associated with AD, the recent progress in research on the drug development to treat AD, especially on the discovery of natural product derivatives to inhibit Aβ peptide aggregation as well as the design and synthesis of Aβ peptide aggregation inhibitors to treat AD.

NOTCH signaling: Journey of an evolutionarily conserved pathway in driving tumor progression and its modulation as a therapeutic target

Notch signaling, an evolutionarily conserved signaling cascade, is critical for normal biological processes of cell differentiation, development, and homeostasis. Deregulation of the Notch signaling pathway has been associated with tumor progression. Thus, Notch presents as an interesting target for a variety of cancer subtypes and its signaling mechanisms have been actively explored from the therapeutic viewpoint. However, besides acting as an oncogene, Notch pathway can possess also tumor suppressive functions, being implicated in inhibition of cancer development. Given such interesting dual and dynamic role of Notch, in this review, we discuss how the evolutionarily conserved Notch signaling pathway drives hallmarks of tumor progression and how it could be targeted for a promising treatment and management of cancer. In addition, the up-to-date information on the inhibitors currently under clinical trials for Notch targets is presented along with how NOTCH inhibitors can be used in conjunction with established chemotherapy/radiotherapy regimes.

Role of Hypoxia Inducible Factor-1α in Alzheimer's Disease

Amyloid-β (Aβ) peptides and hyperphosphorylated tau protein are the most important pathological markers of Alzheimer's disease (AD). Neuroinflammation and oxidative stress are also involved in the development and pathological mechanism of AD. Hypoxia inducible factor-1α (HIF-1α) is a transcriptional factor responsible for cellular and tissue adaption to low oxygen tension. Emerging evidence has revealed HIF-1α as a potential medicinal target for neurodegenerative diseases. On the one hand, HIF-1α increases AβPP processing and Aβ generation by promoting β/γ-secretases and suppressing α-secretases, inactivates microglia and reduces their activity, contributes to microglia death and neuroinflammation, which promotes AD pathogenesis. On the other hand, HIF-1α could resist the toxic effect of Aβ, inhibits tau hyperphosphorylation and promotes microglial activation. In summary, this review focuses on the potential complex roles and the future perspectives of HIF-1α in AD, in order to provide references for seeking new drug targets and treatment methods for AD.

[Involvement of Notch1 and ALK4/5 Signaling Pathways in Renal Tubular Cell Death: Their Application to Clarification of Cadmium Toxicity]

Renal tubular cell death is caused by various extracellular stresses including toxic amounts of cadmium, an occupational and environmental pollutant metal, and is responsible for renal dysfunction. While cadmium exposure disrupts many intracellular signaling pathways, the molecular mechanism underlying cadmium-induced renal tubular cell death has not yet been fully elucidated. We have recently identified two important intracellular signaling pathways that promote cadmium-induced renal tubular cell death: the Notch1 signaling and activin receptor-like kinase (ALK) 4/5 signaling (also known as the activin-transforming growth factor β receptor pathways). In this review paper, we introduce our previous experimental findings, focusing on Notch1 and ALK4/5 signaling pathways, which may uncover the molecular mechanisms involved in cadmium-induced renal tubular cell death.

Molecular Mechanisms and Genetics of Oxidative Stress in Alzheimer's Disease

Alzheimer’s disease is the most common neurodegenerative disorder that can cause dementia in elderly over 60 years of age. One of the disease hallmarks is oxidative stress which interconnects with other processes such as amyloid-β deposition, tau hyperphosphorylation, and tangle formation. This review discusses current thoughts on molecular mechanisms that may relate oxidative stress to Alzheimer’s disease and identifies genetic factors observed from in vitro, in vivo, and clinical studies that may be associated with Alzheimer’s disease-related oxidative stress.

Correlation between the HIF-1α/Notch signaling pathway and Modic changes in nucleus pulposus cells isolated from patients with low back pain

BACKGROUND

The HIF-1α/Notch signaling pathway regulates cell proliferation, apoptosis, and metabolism in the intervertebral discs (IVDs) and is implicated in disc degeneration. The nucleus pulposus (NP) is an important structure adjacent to the IVDs. However, the role of the HIF-1α/Notch signaling pathway in NP cells obtained from patients with different Modic changes (MCs) remains unclear. The purpose of the present study was to investigate the role of HIF-1α and components of the Notch pathway in the NP obtained from patients with various MCs.

METHODS

A total of 85 NP tissue samples were collected from patients undergoing diskectomy for the treatment of low back pain. The NP tissues were divided into four groups based on the adjacent endplate degeneration, namely, MC I, II, III, and negative MC groups. The expression of HIF-1α and Notch-related components was measured and compared.

RESULTS

The expression of HIF-1α, Notch1, and Notch2 was gradually increased in the MC I and MC II groups compared with that in the negative MC group. HIF-1α and Notch-related components were rarely detected in the MC III group.

CONCLUSIONS

The expression of HIF-1α/Notch increased in the NP cells of patients with MC I and MC II. HIF-1α and Notch-related components are potential biomarkers and the HIF-1α/Notch signaling pathway may serve as a promising therapeutic target for disc degeneration in patients with MCs.

SERP1 is an assembly regulator of γ-secretase in metabolic stress conditions

The enzyme γ-secretase generates β-amyloid (Aβ) peptides by cleaving amyloid protein precursor (APP); the aggregation of these peptides is associated with Alzheimer's disease (AD). Despite the development of various γ-secretase regulators, their clinical use is limited by coincident disruption of other γ-secretase-regulated substrates, such as Notch. Using a genome-wide functional screen of γ-secretase activity in cells and a complementary DNA expression library, we found that SERP1 is a previously unknown γ-secretase activator that stimulates Aβ generation in cells experiencing endoplasmic reticulum (ER) stress, such as is seen with diabetes. SERP1 interacted with a subcomplex of γ-secretase (APH1A/NCT) through its carboxyl terminus to enhance the assembly and, consequently, the activity of the γ-secretase holoenzyme complex. In response to ER stress, SERP1 preferentially recruited APP rather than Notch into the γ-secretase complex and enhanced the subcellular localization of the complex into lipid rafts, increasing Aβ production. Moreover, SERP1 abundance, γ-secretase assembly, and Aβ production were increased both in cells exposed to high amounts of glucose and in diabetic AD model mice. Conversely, Aβ production was decreased by knocking down SERP1 in cells or in the hippocampi of mice. Compared to postmortem samples from control individuals, those from patients with AD showed increased SERP1 expression in the hippocampus and parietal lobe. Together, our findings suggest that SERP1 is an APP-biased regulator of γ-secretase function in the context of cell stress, providing a possible molecular explanation for the link between diabetes and sporadic AD.

The Role of a Neurovascular Signaling Pathway Involving Hypoxia-Inducible Factor and Notch in the Function of the Central Nervous System

In the neurovascular unit, the neuronal and vascular systems communicate with each other. O₂ and nutrients, reaching endothelial cells (ECs) through the blood stream, spread into neighboring cells, such as neural stem cells, and neurons. The proper function of neural circuits in adults requires sufficient O₂ and glucose for their metabolic demands through angiogenesis. In a central nervous system (CNS) injury, such as glioma, Parkinson’s disease, and Alzheimer’s disease, damaged ECs can contribute to tissue hypoxia and to the consequent disruption of neuronal functions and accelerated neurodegeneration. This review discusses the current evidence regarding the contribution of oxygen deprivation to CNS injury, with an emphasis on hypoxia-inducible factor (HIF)-mediated pathways and Notch signaling. Additionally, it focuses on adult neurological functions and angiogenesis, as well as pathological conditions in the CNS. Furthermore, the functional interplay between HIFs and Notch is demonstrated in pathophysiological conditions.

miR-151-5p modulates APH1a expression to participate in contextual fear memory formation

Long-term memory formation requires gene expression and new protein synthesis. MicroRNAs (miRNAs), a family of small non-coding RNAs that inhibit target gene mRNA expression, are involved in new memory formation. In this study, elevated miR-151-5p (miR-151) levels were found to be responsible for hippocampal contextual fear memory formation. Using a luciferase reporter assay, we demonstrated that miR-151 targets APH1a, a protein that has been identified as a key factor in γ-secretase activity, namely APH1a. Blocking miR-151 can upregulate APH1a protein levels and subsequently impair hippocampal fear memory formation. These results indicate that miR-151 is involved in hippocampal contextual fear memory by inhibiting APH1a protein expression. This work provides novel evidence for the role of miRNAs in memory formation and demonstrates the implication of APH1a protein in miRNA processing in the adult brain.

What are the links between hypoxia and Alzheimer's disease?

Alzheimer's disease (AD) is the most common neurodegenerative disease. Histological characterization of amyloid plaques and neurofibrillary tangles in the brains of AD patients, alongside genetic studies in individuals suffering the familial form of the disease, has fueled the accumulation of the amyloid-β protein as the initial pathological trigger of disease. Association studies have recently showed that cerebral hypoxia, via both genetic and epigenetic mechanisms, increase amyloid-β deposition by altering expression levels of enzymes involved in the production/degradation of the protein. Furthermore, hypoxia has also been linked to neuronal and glial-cell calcium dysregulation through formation of calcium-permeable pores, dysregulated glutamate signaling, and intracellular calcium-store dysfunction. Hypoxia has also been strongly linked to neuroinflammation; however, this relationship to AD has not been thoroughly discussed in the literature. Here, we highlight and organize critical research evidence showing that in both hypoxic and AD brains, there are similarities in terms of 1) the substances mediating/modulating the neuroinflammatory environment and 2) the immune cells that drive the formation of these substances.

Dysregulation of Neuronal Iron Homeostasis as an Alternative Unifying Effect of Mutations Causing Familial Alzheimer's Disease

The overwhelming majority of dominant mutations causing early onset familial Alzheimer’s disease (EOfAD) occur in only three genes, PSEN1, PSEN2, and APP. An effect-in-common of these mutations is alteration of production of the APP-derived peptide, amyloid β (Aβ). It is this key fact that underlies the authority of the Amyloid Hypothesis that has informed Alzheimer’s disease research for over two decades. Any challenge to this authority must offer an alternative explanation for the relationship between the PSEN genes and APP. In this paper, we explore one possible alternative relationship – the dysregulation of cellular iron homeostasis as a common effect of EOfAD mutations in these genes. This idea is attractive since it provides clear connections between EOfAD mutations and major characteristics of Alzheimer’s disease such as dysfunctional mitochondria, vascular risk factors/hypoxia, energy metabolism, and inflammation. We combine our ideas with observations by others to describe a “Stress Threshold Change of State” model of Alzheimer’s disease that may begin to explain the existence of both EOfAD and late onset sporadic (LOsAD) forms of the disease. Directing research to investigate the role of dysregulation of iron homeostasis in EOfAD may be a profitable way forward in our struggle to understand this form of dementia.

Effects and Mechanism of Huannao Yicong Decoction Extract on the Ethology of Transgenic APP/PS1 Mice

To investigate the mechanism of Huannao Yicong Decoction (HYD) extract on improving of learning memory of transgenic amyloid precursor protein (APP)/presenilin 1 (PS1) mice, we randomly divided 60 transgenic APP/PS1 mice of 3 months old into 4 groups: the model group, the Donepezil group, the HYD-L group, and the HYD-H group, with 15 C57BL/6J mice of the same genetic background as the control group. These mice were gavaged for 6 months in a row. The results showed that the latency was significantly shortened and the number of passing through the original platform was increased. HYD extract can increase the amount of neurons and improve the morphological structure of Nissl body obviously. The γ-secretase activity and the expression of phosphorylated APP, Aβ1-40, and Aβ1-42 in hippocampal CA1 were significantly decreased. The expressions of protein and mRNA of PEN-2 and CREB in hippocampal were significantly downregulated. These results demonstrated that HYD extract can improve the memory ability of transgenic APP/PS1 mice, which was related to the protection of neurons and structure of Nissl body, reducing cleavage of APP and production of Aβ and inhibiting the activity of γ-secretase by decreasing CREB activity because of downregulated expression of PEN-2.

Hypoxia in CNS Pathologies: Emerging Role of miRNA-Based Neurotherapeutics and Yoga Based Alternative Therapies

Cellular respiration is a vital process for the existence of life. Any condition that results in deprivation of oxygen (also termed as hypoxia) may eventually lead to deleterious effects on the functioning of tissues. Brain being the highest consumer of oxygen is prone to increased risk of hypoxia-induced neurological insults. This in turn has been associated with many diseases of central nervous system (CNS) such as stroke, Alzheimer's, encephalopathy etc. Although several studies have investigated the pathophysiological mechanisms underlying ischemic/hypoxic CNS diseases, the knowledge about protective therapeutic strategies to ameliorate the affected neuronal cells is meager. This has augmented the need to improve our understanding of the hypoxic and ischemic events occurring in the brain and identify novel and alternate treatment modalities for such insults. MicroRNA (miRNAs), small non-coding RNA molecules, have recently emerged as potential neuroprotective agents as well as targets, under hypoxic conditions. These 18-22 nucleotide long RNA molecules are profusely present in brain and other organs and function as gene regulators by cleaving and silencing the gene expression. In brain, these are known to be involved in neuronal differentiation and plasticity. Therefore, targeting miRNA expression represents a novel therapeutic approach to intercede against hypoxic and ischemic brain injury. In the first part of this review, we will discuss the neurophysiological changes caused as a result of hypoxia, followed by the contribution of hypoxia in the neurodegenerative diseases. Secondly, we will provide recent updates and insights into the roles of miRNA in the regulation of genes in oxygen and glucose deprived brain in association with circadian rhythms and how these can be targeted as neuroprotective agents for CNS injuries. Finally, we will emphasize on alternate breathing or yogic interventions to overcome the hypoxia associated anomalies that could ultimately lead to improvement in cerebral perfusion.

Involvement of Notch1 signaling in malignant progression of A549 cells subjected to prolonged cadmium exposure

Cadmium exposure is known to increase lung cancer risk, but the underlying molecular mechanisms in cadmium-stimulated progression of malignancy are unclear. Here, we examined the effects of prolonged cadmium exposure on the malignant progression of A549 human lung adenocarcinoma cells and the roles of Notch1, hypoxia-inducible factor 1α (HIF-1α), and insulin-like growth factor 1 receptor (IGF-1R)/Akt/extracellular signal-regulated kinase (ERK)/p70 S6 kinase 1 (S6K1) signaling pathways. Exposing A549 cells to 10 or 20 μm cadmium chloride (CdCl2) for 9-15 weeks induced a high proliferative potential, the epithelial-mesenchymal transition (EMT), stress fiber formation, high cell motility, and resistance to antitumor drugs. Of note, the CdCl2 exposure increased the levels of the Notch1 intracellular domain and of the downstream Notch1 target genes Snail and Slug. Strikingly, siRNA-mediated Notch1 silencing partially suppressed the CdCl2-induced EMT, stress fiber formation, high cell motility, and antitumor drug resistance. In addition, we found that prolonged CdCl2 exposure induced reduction of E-cadherin in BEAS-2B human bronchial epithelial cells and antitumor drug resistance in H1975 human tumor-derived non-small-cell lung cancer cells depending on Notch1 signaling. Moreover, Notch1, HIF-1α, and IGF-1R/Akt/ERK/S6K1 activated each other to induce EMT in the CdCl2-exposed A549 cells. These results suggest that Notch1, along with HIF-1α and IGF-1R/Akt/ERK/S6K1 signaling pathways, promotes malignant progression stimulated by prolonged cadmium exposure in this lung adenocarcinoma model.

The interplay between the cellular hypoxic response and Notch signaling

The ability to sense and adapt to low oxygen levels (hypoxia) is central for most organisms and cell types. At the center of this process is a molecular mechanism, the cellular hypoxic response, in which the hypoxia inducible factors (HIFs) are stabilized by hypoxia, allowing the HIF proteins to act as master transcriptional regulators to adjust the cell to a low oxygen environment. In recent years, it has become increasingly appreciated that the cellular hypoxic response does not always operate in splendid isolation, but intersects with signaling mechanisms such as Notch signaling, a key regulatory signaling mechanism operating in most cell types controlling stem cell maintenance and differentiation. In this review, which is dedicated to the memory of Lorenz Poellinger,¹ we discuss how the intersection between Notch and the cellular hypoxic response was discovered and our current understanding of the molecular basis for the cross-talk. We also provide examples of where Notch and hypoxia intersect in various physiological and disease contexts.

Huannao Yicong Formula () regulates γ-secretase activity through APH-1 and PEN-2 gene ragulation pathways in hippocampus of APP/PS1 double transgenic mice

OBJECTIVE

To observe the effects of Huannao Yicong Formula (, HYF) on learning and memory and it's regulating effect on γ-secretase related anterior pharynx defective 1 (APH-1), presenilin enhancer-2 (PEN-2) signaling pathway, so as to discuss and further clarify the mechanism of HYF on Alzheimer's disease.

METHODS

Sixty APP/PS1 transgenic mice, randomly allocated into 4 groups, the model group, the donepezil group (0.65 mg/kg), HYF low-dose group (HYF-L, 5.46 g/kg) and HYF high-dose group (HYF-H, 10.92 g/kg), 15 for each group. Another 15 C57BL/6J mice with the same age and same genetic background were allocated into the control group, proper dosage of drugs or distilled water were given by intragastric administration once daily for 12 weeks. After 12 weeks of administration, the learning and memory abilities of mice in each group was evaluated by the morris water maze test, amyloid precursor protein (APP), Aβ_1-40 and Aβ_1-42 levels in hippocampus were detected by enzyme-linked immunosorbent assay, γ-secretase was detected by dual luciferase assaying, the levels of APH-1a, hypoxia-inducible factor 1α (HIF-1α), cAMP response element-binding protein (CREB) and PEN-2 and their mRNA expression was measured by Western blot and real-time polymerase chain reaction.

RESULTS

HYF can ameliorate learning and memory deficits in APP/PS1 transgenic mice by decreasing the escape latency, improving the number of platform crossing and swimming speed (P<0.01, P<0.05). HYF can decrease the levels of APP, Aβ_1-40, Aβ_1-42 and the activity of γ-secretase in hippocampus of Alzheimer's disease model mice. HYF can down-regulate the levels of CREB and PEN-2 and the expression of their mRNA.

CONCLUSION

HYF can improve the learning and memory ability by inhibiting the activity of γ-secretase through the CREB/PEN-2 signaling pathway, and this may be one of the therapeutic mechanisms of HYF in Alzheimer's disease.

Acute and Chronic Sustained Hypoxia Do Not Substantially Regulate Amyloid-β Peptide Generation In Vivo

Background

Recent epidemiological evidence has linked hypoxia with the development of Alzheimer disease (AD). A number of in vitro and in vivo studies have reported that hypoxia can induce amyloid-β peptide accumulation through various molecular mechanisms including the up-regulation of the amyloid-β precursor protein, the β-secretase Bace1, or the γγ-secretase complex components, as well as the down-regulation of Aβ-degrading enzymes.

Objectives

To investigate the effects of acute and chronic sustained hypoxia in Aβ generation in vivo.

Methods

2–3 month-old C57/Bl6J wild-type mice were exposed to either normoxia (21% O₂) or hypoxia (9% O₂) for either 4 to 72 h (acute) or 21–30 days (chronic sustained) in a hermetic chamber. Brain mRNA levels of Aβ-related genes were measured by quantitative real-time PCR, whereas levels of Bace1 protein, full length AβPP, and its C-terminal fragments (C99/C88 ratio) were measured by Western blot. In addition, 8 and 14-month-old APP/PS1 transgenic mice were subjected to 9% O₂ for 21 days and levels of Aβ₄₀, Aβ₄₂, full length AβPP, and soluble AβPPα (sAβPPα) were measured by ELISA or WB.

Results

Hypoxia (either acute or chronic sustained) did not impact the transcription of any of the Aβ-related genes in young wild-type mice. A significant reduction of Bace1 protein level was noted with acute hypoxia for 16 h but did not correlate with an increased level of full length AβPP or a decreased C99/C83 ratio. Chronic sustained hypoxia did not significantly alter the levels of Bace1, full length AβPP or the C99/C83 ratio. Last, chronic sustained hypoxia did not significantly change the levels of Aβ₄₀, Aβ₄₂, full length AβPP, or sAβPPα in either young or aged APP/PS1 mice.

Discussion

Our results argue against a hypoxia-induced shift of AβPP proteolysis from the non-amyloidogenic to the amyloidogenic pathways. We discuss the possible methodological caveats of previous in vivo studies.

Appoptosin interacts with mitochondrial outer-membrane fusion proteins and regulates mitochondrial morphology

Mitochondrial morphology is regulated by fusion and fission machinery. Impaired mitochondria dynamics cause various diseases, including Alzheimer's disease. Appoptosin (encoded by SLC25A38) is a mitochondrial carrier protein that is located in the mitochondrial inner membrane. Appoptosin overexpression causes overproduction of reactive oxygen species (ROS) and caspase-dependent apoptosis, whereas appoptosin downregulation abolishes β-amyloid-induced mitochondrial fragmentation and neuronal death during Alzheimer's disease. Herein, we found that overexpression of appoptosin resulted in mitochondrial fragmentation in a manner independent of its carrier function, ROS production or caspase activation. Although appoptosin did not affect levels of mitochondrial outer-membrane fusion (MFN1 and MFN2), inner-membrane fusion (OPA1) and fission [DRP1 (also known as DNM1L) and FIS1] proteins, appoptosin interacted with MFN1 and MFN2, as well as with the mitochondrial ubiquitin ligase MITOL (also known as MARCH5) but not OPA1, FIS1 or DRP1. Appoptosin overexpression impaired the interaction between MFN1 and MFN2, and mitochondrial fusion. By contrast, co-expression of MFN1, MITOL and a dominant-negative form of DRP1, DRP1(K38A), partially rescued appoptosin-induced mitochondrial fragmentation and apoptosis, whereas co-expression of FIS1 aggravated appoptosin-induced apoptosis. Together, our results demonstrate that appoptosin can interact with mitochondrial outer-membrane fusion proteins and regulates mitochondrial morphology.

HIF-1α Inhibition Sensitized Pituitary Adenoma Cells to Temozolomide by Regulating Presenilin 1 Expression and Autophagy

Pituitary adenomas usually develop temozolomide resistance, which could compromise the anticancer effects of temozolomide. Suppression of hypoxia-inducible factor 1α has been shown to sensitize glioblastoma cells to temozolomide treatment according to previous reports. However, whether and how the suppression of hypoxia-inducible factor 1α could sensitize pituitary adenomas to temozolomide treatment are still poorly understood. In the present study, using hypoxia-inducible factor 1α knockdown strategy, we demonstrated for the first time that hypoxia-inducible factor 1α knockdown could inhibit temozolomide-induced autophagy in rat pituitary adenoma GH3 cells and thus increase antitumor efficacy of temozolomide. Furthermore, we found hypoxia-inducible factor 1α knockdown could block autophagy process through neutralizing lysosomal pH value but not inhibiting autophagy induction. Finally, we found hypoxia-inducible factor 1α could regulate lysosomal pH value through regulating full length presenilin 1 expression, and exogenous reexpression of presenilin 1could restore lysosome acidic levels. Our data indicated hypoxia-inducible factor 1α knockdown could be a potential approach to improve the efficacy of temozolomide therapy for pituitary adenomas.

Hypoxia Affects Neprilysin Expression Through Caspase Activation and an APP Intracellular Domain-dependent Mechanism

While gene mutations in the amyloid precursor protein (APP) and the presenilins lead to an accumulation of the amyloid β-peptide (Aβ) in the brain causing neurodegeneration and familial Alzheimer's disease (AD), over 95% of all AD cases are sporadic. Despite the pathologies being indistinguishable, relatively little is known about the mechanisms affecting generation of Aβ in the sporadic cases. Vascular disorders such as ischaemia and stroke are well established risk factors for the development of neurodegenerative diseases and systemic hypoxic episodes have been shown to increase Aβ production and accumulation. We have previously shown that hypoxia causes a significant decrease in the expression of the major Aβ-degrading enzyme neprilysin (NEP) which might deregulate Aβ clearance. Aβ itself is derived from the transmembrane APP along with several other biologically active metabolites including the C-terminal fragment (CTF) termed the APP intracellular domain (AICD), which regulates the expression of NEP and some other genes in neuronal cells. Here we show that in hypoxia there is a significantly increased expression of caspase-3, 8, and 9 in human neuroblastoma NB7 cells, which can degrade AICD. Using chromatin immunoprecipitation we have revealed that there was also a reduction of AICD bound to the NEP promoter region which underlies the decreased expression and activity of the enzyme under hypoxic conditions. Incubation of the cells with a caspase-3 inhibitor Z-DEVD-FMK could rescue the effect of hypoxia on NEP activity protecting the levels of AICD capable of binding the NEP promoter. These data suggest that activation of caspases might play an important role in regulation of NEP levels in the brain under pathological conditions such as hypoxia and ischaemia leading to a deficit of Aβ clearance and increasing the risk of development of AD.

Non-small-cell lung carcinoma: role of the Notch signaling pathway

Notch signaling plays a pivotal role during embryogenesis. It regulates three fundamental processes: lateral inhibition, boundary formation, and lineage specification. During post-natal life, Notch receptors and ligands control critical cell fate decisions both in compartments that are undergoing differentiation and in pluripotent progenitor cells. First recognized as a potent oncogene in certain lymphoblastic leukemias and mesothelium-derived tissue, the role of Notch signaling in epithelial, solid tumors has been far more controversial. The overall consequence of Notch signaling and which form of the Notch receptor drives malignancy in humans is deeply debated. Most likely, this is due to the high degree of context-dependent effects of Notch signaling. More recently, it has been discovered that Notch (especially Notch-1) can exert different, even opposite effects in the same tissue under differing microenvironmental conditions. Further complicating the understanding of Notch receptors is the recently discovered role for non-canonical Notch signaling. Additionally, the most frequent Notch signaling antagonists used in biological systems have been inhibitors of the transmembrane protease complex γ-secretase, which itself processes a plethora of class one transmembrane proteins and thus cannot be considered a Notch-specific upstream regulator. Here we review the available empirical evidence gathered in recent years concerning Notch receptors and ligands in non-small-cell lung carcinoma (NSCLC). Although an overview of the field reveals seemingly contradicting results, we propose that Notch signaling can be exploited as a therapeutic target in NSCLC and represents a promising complement to the current arsenal utilized to combat this malignancy, particularly in targeting NSCLC tissues under specific environmental conditions, such as hypoxia.

AP4 activates cell migration and EMT mediated by p53 in MDA-MB-231 breast carcinoma cells

Tumor metastasis is the primary cause of mortality in most cancer patients. Before disassociation from the tumors, most of malignant tumor cells undergo the epithelial-mesenchymal transition to break away from the adhesions between the cells and the surrounding extracellular matrix. Recently, activating enhancer-binding protein (AP4) has been shown to be a mediator of EMT in colorectal cancer and high level of AP4 correlates with poor prognosis in cancer patients. It has been found that AP4 upregulates the genes involved in EMT and cell proliferation in colorectal cancer cells and that the aggressive human breast cancer cells MDA-MB-231 are highly metastatic. Therefore, we tested the hypothesis that AP4 may also affect cell migration and EMT in this cell type. Three different assays, including the wound-healing assay, the Boyden chamber assay, and the cell tracking assay, were employed to confirm that AP4 activated both cell migration and invasion. Immunofluorescence staining and Western blot analysis revealed that the cells underwent EMT when AP4 was upregulated. In contrast, overexpression of dominant-negative AP4, lacking the DNA-binding domain, inactivated the DNA-binding ability of endogenous AP4 and led to lower cell motility. Furthermore, we found that AP4 enhanced p53 expression at both transcriptional and translational levels. Knockdown of p53 by siRNA significantly diminished the activation of cell migration by AP4, indicating that AP4 can regulate cell migration via the activity of p53.

Differential roles of Aβ processing in hypoxia-induced axonal damage

Axonopathy is a common and early phase in neurodegenerative and traumatic CNS diseases. Recent work suggests that amyloid β (Aβ) produced from amyloid precursor protein (APP) may be a critical downstream mediator of CNS axonopathy in CNS diseases, particularly those associated with hypoxia. We critically tested this hypothesis in an adult retinal explant system that preserves the three-dimensional organization of the retina while permitting direct imaging of two cardinal features of early-stage axonopathy: axonal structural integrity and axonal transport capacity. Using this system, we found via pharmacological inhibition and genetic deletion of APP that production of Aβ is a necessary step in structural compromise of retinal ganglion cell (RGC) axons induced by the disease-relevant stressor hypoxia. However, identical blockade of Aβ production was not sufficient to protect axons from associated hypoxia-induced reduction in axonal transport. Thus, Aβ mediates distinct facets of hypoxia-induced axonopathy and may represent a functionally selective pharmacological target for therapies directed against early-stage axonopathy in CNS diseases.

Nontranscriptional role of Hif-1α in activation of γ-secretase and notch signaling in breast cancer

γ-Secretase is composed of four proteins that are obligatory for protease activity: presenilin, nicastrin, Aph1, and Pen-2. Despite the progress toward understanding the function of these individual subunits, there is no information available pertaining to the modulation of γ-secretase in response to environmental changes in cells. Here, we show that hypoxia upregulates γ-secretase activity through a direct interaction with Hif-1α, revealing an unconventional function for Hif-1α as an enzyme subunit, which is distinct from its canonical role as a transcription factor. Moreover, hypoxia-induced cell invasion and metastasis are alleviated by either γ-secretase inhibitors or a dominant-negative Notch coactivator, indicating that γ-secretase/Notch signaling plays an essential role in controlling these cellular processes. The present study reveals a mechanism in which γ-secretase can achieve temporal control through conditional interactions with regulatory proteins, such as Hif-1α, under select physiological and pathological conditions.

Quercetin attenuates cell apoptosis of oxidant-stressed SK-N-MC cells while suppressing up-regulation of the defensive element, HIF-1α

Evidence is emerging that reactive oxygen species (ROS)-induced oxidative stress has a crucial role in the pathogenesis of neurodegenerative diseases. To find the effective therapies for neurodegenerative diseases, evaluation of the relevant molecular mechanisms is necessary. In the current study, we investigated the effects of hydrogen peroxide (H2O2)-induced oxidative stress on SK-N-MC cell death with focus on HIF-1α, Foxo3a and Notch1 signaling factors. Our results revealed that H2O2 reduced viability of cells through up-regulation of p53 followed by increase in Bax/Bcl2 ratio. In addition, H2O2 increased intracellular levels of HIF-1α, Foxo-3a and Notch intracellular domain (NICD). However, Quercetin decreased cell contents of HIF-1α, Foxo-3a and NICD as well as pro-apoptotic factors including p53 and Bax compared to H2O2-treated cells. Additionally, we found that HIF-1α down-regulation reduced Foxo3a and NICD contents parallel to up-regulation of p53 and Bax and led to further vulnerability to oxidative stress-induced cell death. In contrast, Notch inhibition resulted in HIF-1α/Foxo3a signaling pathway up-regulation, suggesting the bidirectional crosstalk between HIF-1α and Notch1. These results collectively suggest that ROS are involved in activation of both the defensive and pro-apoptotic pathways encompassing HIF-1α and p53, respectively. Regarding the HIF-1α-mediated neuroprotection role, elucidation of the molecular mechanism would certainly be essential for effective drug design against neurodegenerative diseases.

Epigenetic modifications of chronic hypoxia-mediated neurodegeneration in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder affecting the elderly people. AD is characterized by progressive and gradual decline in cognitive function and memory loss. While familial early-onset AD is usually associated with gene mutations, the etiology of sporadic late-onset form of AD is largely unknown. It has been reported that environmental factors and epigenetic alterations significantly contribute to the process of AD. Our previous studies have documented that chronic hypoxia is one of the environmental factors that may trigger the AD development and aggravate the disease progression. In this review, we will summarize the pathological effects of chronic hypoxia on the onset and development of AD and put forward the possible molecule mechanisms underlying the chronic hypoxia mediated AD pathogenesis. Finally, we propose that epigenetic regulations may represent new opportunity for the therapeutic intervention of this disease.

Valproic acid reduces neuritic plaque formation and improves learning deficits in APP(Swe) /PS1(A246E) transgenic mice via preventing the prenatal hypoxia-induced down-regulation of neprilysin

AIMS

Previously, we have documented that prenatal hypoxia can aggravate the cognitive impairment and Alzheimer's disease (AD) neuropathology in APP(Swe) /PS1(A246E) (APP/PS1) transgenic mice, and valproic acid (VPA) can prevent hypoxia-induced down-regulation of β-amyloid (Aβ) degradation enzyme neprilysin (NEP) in primary neurons. In this study, we have investigated the molecular mechanisms of VPA's anti-AD effects and found that VPA can reduce the prenatal hypoxia-induced neuritic plaque formation and improve the learning deficits in the AD mouse model.

METHODS

The pregnant APP/PS1 transgenic mice were exposed in a hypobaric chamber. Neuritic plaque staining, Morris water maze, and enzyme-linked immunosorbent assay (ELISA) were used to detect the effects of VPA on Aβ neuropathology, learning, and memory. Chromatin immunoprecipitation (ChIP) assays and real-time PCR (RT-PCR) were used to determine the effect of VPA on the histone3 acetylation (H3-Ace).

RESULTS

We found that VPA can inhibit neuritic plaque formation and improve the learning and memory in the prenatal hypoxic APP/PS1 transgenic mice. In addition, VPA treatment can decrease the soluble and insoluble Aβ42 levels and increase the NEP expression via up-regulation of H3-Ace in the APP/PS1 transgenic mice.

CONCLUSION

Valproic acid is able to attenuate the prenatal hypoxia-induced Aβ neuropathology and learning and memory deficits via inhibiting the activation of histone deacetylase 1 (HDAC1), preventing the decrease in H3-Ace in the NEP promoter regions and reducing the down-regulation of NEP.

Transcriptional regulation by hypoxia inducible factors

The cellular response to oxygen deprivation is governed largely by a family of transcription factors known as Hypoxia Inducible Factors (HIFs). This review focuses on the molecular mechanisms by which HIFs regulate the transcriptional apparatus to enable the cellular and organismal response to hypoxia. We discuss here how the various HIF polypeptides, their posttranslational modifications, binding partners and transcriptional cofactors affect RNA polymerase II activity to drive context-dependent transcriptional programs during hypoxia.

High expression of AP-4 predicts poor prognosis for hepatocellular carcinoma after curative hepatectomy

The aim of this study was to evaluate the association between activating enhancer binding protein 4 (AP-4) tissue expression and patient prognosis in hepatocellular carcinoma (HCC). The levels of AP-4 mRNA and protein in tumor and para-tumor tissue were evaluated in 30 HCC cases by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. Additionally, AP-4 protein expression in 112 HCC was analyzed by immunohistochemistry. The correlation of AP-4 expression and patients' clinicopathological parameters was evaluated. Survival analysis was performed using the Kaplan-Meier method and Cox's proportional hazards model. By RT-PCR and Western blot, the levels of AP-4 mRNA and protein were significantly higher in HCC, compared to that in para-tumor tissue (p < 0.001). Immunohistochemical staining revealed that AP-4 was highly expressed in 53.6 % of the HCC patients. The AP-4 expression level was closely associated with serum alpha fetoprotein elevation, tumor size, histological differentiation, tumor recurrence, tumor metastasis, and tumor stage. Kaplan-Meier survival analysis showed that a high expression level of AP-4 resulted in a significantly poor prognosis of HCC patients. Multivariate analysis revealed that AP-4 expression level was an independent prognostic parameter for the overall survival rate of HCC patients. These findings provide evidence that a high expression level of AP-4 serves as a biomarker for poor prognosis for HCC. Thus, we speculate that AP-4 may be a potential target of antiangiogenic therapy for HCC.

Mutant amyloid precursor protein differentially alters adipose biology under obesogenic and non-obesogenic conditions

Mutations in amyloid precursor protein (APP) have been most intensely studied in brain tissue for their link to Alzheimer’s disease (AD) pathology. However, APP is highly expressed in a variety of tissues including adipose tissue, where APP is also known to exhibit increased expression in response to obesity. In our current study, we analyzed the effects of mutant APP (E693Q, D694N, K670N/M671L) expression toward multiple aspects of adipose tissue homeostasis. These data reveal significant hypoleptinemia, decreased adiposity, and reduced adipocyte size in response to mutant APP, and this was fully reversed upon high fat diet administration. Additionally, mutant APP was observed to significantly exacerbate insulin resistance, triglyceride elevations, and macrophage infiltration of adipose tissue in response to a high fat diet. Taken together, these data have significant implications for linking mutant APP expression to adipose tissue dysfunction and global changes in endocrine and metabolic function under both obesogenic and non-obesogenic conditions.

The updated biology of hypoxia-inducible factor

Oxygen is essential for eukaryotic life and is inextricably linked to the evolution of multicellular organisms. Proper cellular response to changes in oxygen tension during normal development or pathological processes, such as cardiovascular disease and cancer, is ultimately regulated by the transcription factor, hypoxia-inducible factor (HIF). Over the past decade, unprecedented molecular insight has been gained into the mammalian oxygen-sensing pathway involving the canonical oxygen-dependent prolyl-hydroxylase domain-containing enzyme (PHD)-von Hippel-Lindau tumour suppressor protein (pVHL) axis and its connection to cellular metabolism. Here we review recent notable advances in the field of hypoxia that have shaped a more complex model of HIF regulation and revealed unique roles of HIF in a diverse range of biological processes, including immunity, development and stem cell biology.

Down-regulation of AP-4 inhibits proliferation, induces cell cycle arrest and promotes apoptosis in human gastric cancer cells

Background

AP-4 belongs to the basic helix-loop-helix leucine-zipper subgroup; it controls target gene expression, regulates growth, development and cell apoptosis and has been implicated in tumorigenesis. Our previous studies indicated that AP-4 was frequently overexpressed in gastric cancers and may be associated with the poor prognosis. The purpose of this study is to examine whether silencing of AP-4 can alter biological characteristics of gastric cancer cells.

Methods

Two specific siRNAs targeting AP-4 were designed, synthesized, and transfected into gastric cancer cell lines and human normal mucosa cells. AP-4 expression was measured with real-time quantitative PCR and Western blot. Cell proliferation and chemo-sensitivity were detected by CCK-8 assay. Cell cycle assay and apoptosis assay were performed by flow cytometer, and relative expression of cell cycle regulators were detected by real-time quantitative PCR and Western blot, expression of the factors involved in the apoptosis pathway were examined in mRNA and protein level.

Results

The expression of AP-4 was silenced by the siRNAs transfection and the effects of AP-4 knockdown lasted 24 to 96 hrs. The siRNA-mediated silencing of AP-4 suppressed the cellular proliferation, induced apoptosis and sensitized cancer cells to anticancer drugs. In addition, the expression level of p21, p53 and Caspase-9 were increased when AP-4 was knockdown, but the expression of cyclin D1, Bcl-2 and Bcl-x_L was inhibited. It didn't induce cell cycle arrest when AP-4 was knockdown in p53 defect gastric cancer cell line Kato-III.

Conclusions

These results illustrated that gene silencing of AP-4 can efficiently inhibited cell proliferation, triggered apoptosis and sensitized cancer cells to anticancer drugs in vitro, suggesting that AP-4 siRNAs mediated silencing has a potential value in the treatment of human gastric cancer.

Neuroprotection and neurodegeneration in Alzheimer's disease: role of cardiovascular disease risk factors, implications for dementia rates, and prevention with aerobic exercise in african americans

Prevalence of Alzheimer's disease (AD) will reach epidemic proportions in the United States and worldwide in the coming decades, and with substantially higher rates in African Americans (AAs) than in Whites. Older age, family history, low levels of education, and ɛ4 allele of the apolipoprotein E (APOE) gene are recognized risk factors for the neurodegeneration in AD and related disorders. In AAs, the contributions of APOE gene to AD risk continue to engender a considerable debate. In addition to the established role of cardiovascular disease (CVD) risk in vascular dementia, it is now believed that CVD risk and its endophenotype may directly comediate AD phenotype. Given the pleiotropic effects of APOE on CVD and AD risks, the higher rates of CVD risks in AAs than in Whites, it is likely that CVD risks contribute to the disproportionately higher rates of AD in AAs. Though the advantageous effects of aerobic exercise on cognition is increasingly recognized, this evidence is hardly definitive, and data on AAs is lacking. In this paper, we will discuss the roles of CVD risk factors in the development of AD and related dementias, the susceptibility of these risk factors to physiologic adaptation, and fitness-related improvements in cognitive function. Its relevance to AD prevention in AAs is emphasized.